ng-select - Large data set slow loading

I am using the ng-select library for Angular 5 at version 1.4.2. I have a large data set of about 700 records. The data in my select drop down appears fine but appears after a few seconds only. Is there a way to make it appear quicker?

I have had a look into virtual scrolling. Is this an option? I also need to be able to do searching and in the demo at https://ng-select.github.io/ng-select#/virtual-scroll I am not sure if this works.

Here is the HTML for my select box:

<ng-select [items]="clients| async | orderBy : ['name']"
           [closeOnSelect]="true"
           [searchable]="true"
           bindValue="id.clientID"
           bindLabel="name"
           placeholder="Select a Client..."
           notFoundText=""
           [(ngModel)]="selectedClient"
           name="client">
</ng-select>

Here is my Angular component code that loads this data on initialization:

ngOnInit() {
    this.clients = this.clientService.getClients();
}

clients is defined as

clients: Observable<Client[]>;